ATRA treatment selectively induced cell growth inhibition and death in RARα2⁺ MM cells. RARα2⁺ ARK, KMS11, and OPM2 cells, and RARα2⁻ ARP.1, OCI-MY5, CAG, and XG1 cells were treated with ATRA (10⁻⁶ M) for 4 days in the cultures. Cell proliferation (A) and death (B) were evaluated. Untreated cells were used as controls. Results are expressed as means plus SD of 3 independent experiments. *P < .05. (C) RT-PCR examined RARα2 mRNA in RARα2-overexpressing cells (R2). Wild-type (WT) and EV-transfected cells were used as controls; RARα2-overexpressing ARP.1, OCI-MY5, and XG1 cells were treated with ATRA (10⁻⁶ M) for 4 days in the cultures. Cell proliferation (D) and cell death (E) were evaluated. WT and EV cells with or without ATRA treatment were used as controls. R2 cells without ATRA treatment were also used as control. Results are expressed as means SD of 3 independent experiments. *P < .05.